by Robin Riordan
Craters are among the most fascinating features of many moons and planets. Many are caused by asteroid impacts! In this activity, your students experiment to find out more about what causes the various features of impact craters, including the rim of mountains around the edge, and the streaks or rays that fan out from large craters. What they learn in this activity about our own Moon, Luna, they can later compare and contrast to what they find out about the moons of Jupiter and our own planet Earth.
What You Need
For the Class:
- Transparency images of the Earth’s Moon and a closeup of a large lunar crater. You can view pictures of the full moon and crater Copernicus by clicking on these hyperlinks. Print them out on your classroom printer and photocopy them on to transparency paper.
- 1 overhead projector and screen
- 1or more brooms or whisk brooms to clean up spills
- 1 pair of scissors or a paper cutter (to cut the centimeter rulers off the student data sheets)
- 1 container instant chocolate milk powder. (Note: Real cocoa has also been used, but it tends to clump and to over-darken the flour too quickly.)
- three or four 5-pound packages of white flour
For each team of 4 students:
- 1 shallow basin (to be filled with about 3 to 5 inches of flour) Examples: a dishpan, a heavy aluminum roasting pan, or cardboard box. To be sure to have enough, you may want to ask a student from each group to bring in a dishpan from home for the day of the activity. They don’t all have to be the same size.
- 1 cup or small plastic container (to be filled about one-third full with powdered instant chocolate milk mix)
- an old newspaper
- three rocks: small, medium, and large with diameters about: .5cm (1/4 inch), 2cm (3/4 inch) and 4cm (about 1 ½ inches)
- 1 spoon(plastic or metal)
- 1 “Craters” activity sheet
- Before the day of the activity, collect and sort the rocks needed for all the groups.
- Make one copy of the “Craters” data sheet for each student. With scissors or a paper cutter, cut the centimeter rulers form the bottom of the data sheets.
- Assemble sets of materials for the teams: newspaper, a dishpan filled with flour 3 to 5 inches deep, a cup about one-third full of instant chocolate milk mix, and three different-sized rocks. Have data sheets, paper rulers, and pencils handy, but separate from the other materials. Keep one set of all the materials handy near the place where you will demonstrate the activity.
- Try the cratering activity yourself so you will know what to expect. Weather permitting, some teachers prefer to do this activity outside for more space and less cleanup. Decide whether your students will do the activity indoors or outdoors.
- In these activities, there is first free exploration and then more focused cratering experiments that use data sheets. You will need to get the attention of your whole class for instructions before they begin both the free exploration and the more focused experiments. We recommend gathering your class away from the materials for both of these introductions. Some classrooms do not have enough space for students to leave the materials and gather for the second set of instructions. If this is the case, consider explaining all parts of the activity before distributing any of the materials. Read over the lesson, and decide if you’ll need to modify your introduction in this way.
- Set up the overhead projector and have the transparencies ready for viewing (front side of the Moon and close-up of a crater). Prepare to darken the room by drawing curtains or shades.
Meteors and Craters
- Tell the class that the name of Earth’s Moon is Luna. Encourage students to begin thinking about Luna by asking them to image landing on the Moon’s surface.
- What do you imagine the surface of our Moon is like?
- What would it feel like to be walking on Luna?
- What would you see around you?
- Dim the room lights and turn on the overhead projector. Show the image of the Earth’s Moon. (This is the side of the Moon that always faces Earth.) Tell them that this is how our Moon would look if viewed through a small telescope.
- Ask, “What do you see on the Moon’s surface?” Accept their responses (for example, light areas, dark areas, craters etc.). If somebody mentions craters, have them point out an example of one for the class. If craters are not mentioned, point out a large one and identify it as a crater. Explain that craters are big “dents” or holes in the Moon’s surface. Do not go into detail about other surface features at this time.
- Turn on the room lights and turn off the overhead projector. Ask, “What causes craters on the Moon?” (Most students will have an answer for this question and may use terms such as: meteors, asteroids, big rocks, comets, etc.)
- Ask students if they know what a meteor is. (A rock from space falling toward a planet or moon.) Since the terms are often confusing, you may wish to explain that a meteoroid is a rock in space: a meteor is the same rock falling through the Earth’s atmosphere, creating a streak of light (sometimes also called a “shooting star”). Fragments of meteors that survive the fiery trip through the atmosphere and land on the surface are called meteorites. However, it is not important for students to memorize these terms
- Ask your students if there are craters on the Earth. If anybody has visited a crater site, have them share their experience with the class. Explain that the Earth has many craters. Some were caused by volcanoes. Others, called impact craters, were made by meteorites. Ask, “Why do we see very few impact craters on the Earth?” (The Earth has rain and wind which erode away the evidence of most craters.)
- Explain that Earth’s atmosphere prevents small meteors from reaching the surface, because when a meteor falls toward a planet with an atmosphere, it “rubs” against the air.
- Have your students rub their hands together quickly for about ten seconds (counting “one-thousand-one, one-thousand-two,” etc.) Ask what they feel. (Heat.) Tell them if they could rub fast enough they could create enough friction to light a fire.
- Explain that, in a similar way, the flash of light they see from a “shooting star” or meteor is a white-hot glow produced by the heat of friction between the meteor and the air, as the meteor falls through the Earth’s atmosphere. Many smaller meteors burn up before hitting the Earth’s surface—that doesn’t happen on the Moon, because the Moon has no air to rub against, which is one reason why the Moon has lots of craters.
- Tell the class that they will now investigate what happens when a meteoroid hits a solid surface like that of the Moon.
- Tell the students that they will use a pan of flour and three different size rocks to investigate meteor craters. The flour will represent the surface of the Moon and the rocks will be the “meteoroids.”
- Demonstrate the technique:
- Place an old newspaper and a pan of flour on the floor near your feet.
- Sprinkle a light coating of instant chocolate milk mix on the surface of the flour to create a contrast that will help make changes more visible.
- Hold out a medium-sized rock at about shoulder level. Don’t actually drop the rock. Tell the students that they are to drop, NOT THROW, their rock onto the flour.
- After they drop their “meteoroid” they observe what happens to the flour.
- Ask, “What do you think will happen?” and have several students make predictions.
- Explain that they will work in groups, and take turns dropping the rocks into the flour. Point out that they need to observe very carefully so they can describe what happens on impact and what features are created on the “lunar” surface. It’s not necessary to smooth the flour and apply chocolate milk mix after each try.It’s okay that there will be chocolate milk powder mixed in the flour as teams repeatedly level and resurface the flour. If the mixture becomes very dark, or if a team has used up all its chocolate milk powder, suggest they sprinkle flour on the surface instead of the powder to create a contrast.
- Emphasize how important it is to drop the rocks carefully, and never to throw the rocks, or act in any way that is unsafe. (Since flour underfoot can be slippery, if any gets on the floor, it should be swept up immediately. Demonstrate how to sweep flour onto a sheet of newspaper and return it to the basin.)
- If you feel it would be helpful, give the students a few minutes as a whole group to discuss ways to take turns making the craters. You may also want to have them meet in their small groups to agree on a system for taking turns before you distribute their materials.
- Distribute the materials to the teams and let them freely explore the materials and practice making craters for about five minutes. Do not pass out the data sheets yet.
- After free exploration, gather students away from the materials and ask the students: “What did you find out? What Features did your craters have?”
- You may want to have a few volunteers draw what they saw on the chalkboard. As students describe the various features, write some terms on the board. (The impression left on the surface is called a crater basin. Students may have notices a rim around the edge of the basin and streaks or rays that radiated outward from the crater.)
- Explain the procedures for the two experiments, as follows:
- Remind your students that they saw craters of many different sizes on the image of the Moon. Ask, “What might affect how big craters will be?” (Students may suggest meteoroid size or weight, speed at impact, direction, or type of surface material.)
- Explain to the class that the teams will now conduct experiments to find out how two of those factors affect the size of the craters: the size of the meteoroid and the speed of impact. Hold up a data sheet and explain the two experiments:
Experiment 1: Size of Rock
Tell the class that in order to learn more about how the size of the rock affects the size of the crater, teams will make three craters with each of their three rocks (a total of nine craters for Experiment 1). Teams will drop three different size rocks from the same height. They are to drop each rock three times, and record the crater diameter after each drop.
- Ask why it will be important to drop all the rocks from the same height. (Then, if the crater size varies, they’ll know it’s because of the size of the rock). Suggest that they use one team member’s shoulder height as a standard for every trial.
- Demonstrate how to remove the rock from the flour very carefully, so you don’t disturb the crater.
- Show how to measure the diameter of the crater, using a paper centimeter ruler. Show where to record the crater diameters on the data sheet.
- Demonstrate how to jiggle the container back and forth a few times to level the flour, and how to sprinkle more chocolate milk powder on top when the surface needs it.
Experiment 2: Speed of Impact
Explain that this time, the team will choose only one rock to make all their craters, but they will drop the rock from different heights: knee-high, shoulder-high, and as high as they can reach when standing on the floor. Make sure that the students understand that a rock gains speed as it falls, so the farther it falls, the faster it will be going when it hits the flour They will make three craters from each of the three heights. (A total of nine craters for Experiment 2)
- Ask why they should use the same rock when they are experimenting with different speeds of “meteors.” (If they used a different rocks and different heights, they won’t know which made the differences in crater sizes.)
- Point out that knee-high, shoulder-high, and as high as they can reach, may vary for different students, and ask them for ideas about how to keep the height standard on all three tries. (They could take turns dropping the rock, but use one student’s knee, shoulder, and outstretched arm as the standard for all tries.)
- Show where to record all crater diameters in this second experiment.
- Make sure the students understand the two experiments. Hand out the data sheets and paper rulers and have them begin.
- Circulate during the experiments, checking to be sure students are working safely and cooperatively in their teams.
- If a team finishes early, suggest that they extend their investigations in Experiment 2 by, for example, carefully standing on a chair to drop the rock. (Older students may want to extend their investigation by observing or measuring crater depths created by various sizes or speeds of “meteoroids”. The long “rays” that radiate from their “craters” could also be measured.)
- As teams finish, have them return their equipment to the materials area and clean up. Students should keep their data sheets for the discussion.
Discussing the Results:
- Gather the class in the discussion area.
- Have the class look at their data for Experiment 1, comparing meteor sizes, and ask them to describe what they observed and recorded. Ask, “Does the size of the meteoroid have anything to do with the size of the crater?” (Your students’ experimental data is likely to vary, but many students will find that crater size increases with the size of the meteoroid.)
- Ask the students what they can conclude from Experiment 2, about meteors that have struck with different speeds. (Again, student data will vary, but many students will conclude that the faster the meteor, the bigger the crater.) You may want to add that scientists estimate that real craters caused by actual meteor impacts are about 20 times the diameter of the meteor itself.
- Show the picture of Earth’s Moon again. Ask volunteers to point out some of the features of craters on the Moon that they recognize from their experiments.
- Show the close-up transparency of a Moon crater and ask for more observations and comments. Your students may notice that all the lunar craters appear round. No matter the initial shape of the meteor (or the angle of its impact) the resulting explosion will always form a round crater.
If you wanted to land a spacecraft or build a lunar settlement on the Moon, where would you choose? Before real astronauts landed on the Moon, they needed to study a map of the Moon. Hand out a copy of the Moon Map to each student. Project the image of the full moon and have students compare the features on their map with those on the Moon’s surface.
Have the students work in pairs or groups and assign a particular “ocean”, “sea”, or “bay” for them to find. They should locate it first on their map and then identify the corresponding feature on the moon image. Those who finish quickly can practice finding other features. Have volunteers from each group get up and point out their features to the rest of the class. (There are 12 oceans and seas labeled on the map.)
For a more difficult challenge, assign each group a crater or mountain range to find. Invite the students to use their lunar maps when observing the real Moon in the sky. Encourage them to use a pair of binoculars if available. (Through binoculars, the moon-view will match the map, but through a telescope, the image is reversed!).